Reversible Addition-fragmentation Transfer Agent Research Articles

Synthesis of Poly(styrene)-g-Poly(oleic acid) Graft Copolymers via Reversible Addition/Fragmentation Transfer (RAFT) Polymerization Using a Poly Oleic Acid Macro-RAFT Agent

In this study, a new polymeric oleic acid-derived macro addition/fragmentation transfer agent was utilized to produce a poly(styrene)-g-poly(oleic acid) graft copolymer. The double bond of oleic acid was initially saturated with bromine and the condensation polymerization between the carboxylic acid and the bromide resulted in polyoleic acid with pendant bromide groups. Xanthate groups were exchanged with the bromide groups to obtain the poly(oleic acid) macro RAFT agent (Pole-Xa). Poly(styrene)-g-poly(oleic acid) (PS-g-Pole) graft copolymers were synthesized via reversible addition fragmentation transfer (RAFT) polymerization of styrene and the reaction was evaluated in view of the polymerization kinetics. The effects of polymerization temperature and reaction time on graft copolymer yield, conversion and molecular weight were investigated. In the RAFT polymerization of styrene, the rate constant (k) was found to be 1.83 × 10–3 L/mol/dk and 7.27 × 10–4 L/mol/dk for the polymerization temperatures of 80 and 90 °C, respectively. The structural characteristics and thermal properties of the obtained products were characterized using FT-IR, 1H-NMR, GPC, TGA, DSC and SEM–EDX.

Modification of High‐Density Polyethylene through the Grafting of Methyl Methacrylate Using RAFT Technique and Preparation of Its Polymer/Clay Nanocomposites**

AbstractA well‐defined method for discovering an easy and effective strategy through graft copolymer derived from poly (methylmethacrylate) (PMMA) as a monomer, high‐density polyethylene (HDPE) and its organoclay nanocomposite with physicochemical and mechanical properties was successfully prepared by reversible addition‐fragmentation transfer (RAFT) polymerization, and factors organoclay (Cloisite® 20 A) on the terminal features of the obtained graft copolymer were investigated. First, maleic anhydride (MA) was grafted onto HDPE directed by, the inauguration of an anhydride chain with ethanolamine to develop a hydroxylated high‐density polyethylene (HDPE‐OH). After that, the hydroxyl masses were esterified by using RAFT agent, 4‐cyano‐4‐[(phenyl carbon thionyl) sulfanyl valeric acid to obtain HDPE‐CTA macroinitiator. Then, the MMA monomer was grafted onto HDPE via the RAFT method to obtain the HDPE‐g‐PMMA graft copolymer. In the end, HDPE‐g‐PMMA/clay nanocomposite by a solution intercalation method was synthesized. The structures of the, copolymer and nanocomposite were studied by Fourier transform infrared spectroscopy, X‐ray diffraction, and Transmission electron microscopy (TEM) techniques. It explores for the synthesis of HDPE‐g‐PMMA/clay nanocomposites, disclosed a foliated structure. Based on the thermic behavior, synthesized HDPE‐g‐PMMA/clay nanocomposites can display the above thermic solidity with just some extent (5) of organoclay.

EFFECT OF EMULSION SBR PREPARED BY ASYMMETRIC REVERSIBLE ADDITION-FRAGMENTATION TRANSFER AGENT ON PROPERTIES OF SILICA-FILLED COMPOUNDS

ABSTRACT The development of ultra-high-performance tires that satisfy fuel efficiency, traction, handling performance, and abrasion resistance has gained significant importance in the tire industry. Solution SBR has been used as a raw material, owing to its useful characteristics (e.g., narrow dispersity controllable microstructure and chain-end functionalization). In a recent improvement, emulsion SBR (ESBR), a high-molecular-weight compound with narrow dispersity, has been reported for application in the tire tread compounds. In particular, S,S-dibenzyl trithiocarbonate (DBTC) reversible addition-fragmentation transfer (RAFT) ESBR has exhibited excellent abrasion resistance and fuel efficiency in unfilled and carbon black–filled vulcanizates. However, owing to the symmetrical structure of DBTC RAFT ESBR, the polymer chain was shortened by the reaction of a silane coupling agent with trithiocarbonate, leading to poor abrasion resistance and fuel efficiency in the case of silica-filled vulcanizates. In this study, benzyl (4-methoxyphenyl) trithiocarbonate (BMPTC), an asymmetric RAFT agent that promotes unilateral polymer growth, was synthesized and used in the polymerization of BMPTC RAFT ESBR. Chain cleavage was not observed. Upon application to silica-filled vulcanizates, BMPTC RAFT ESBR exhibited improved abrasion resistance (by 9%), improved fuel efficiency (by 20%), and improved wet traction performance (by 10%) compared with the DBTC RAFT ESBR.

Poly(N,N-bis(2-methoxyethyl)acrylamide), a thermoresponsive non-ionic polymer combining the amide and the ethyleneglycolether motifs

Poly(N,N-bis(2-methoxyethyl)acrylamide) (PbMOEAm) featuring two classical chemical motifs from non-ionic water-soluble polymers, namely, the amide and ethyleneglycolether moieties, was synthesized by reversible addition fragmentation transfer (RAFT) polymerization. This tertiary polyacrylamide is thermoresponsive exhibiting a lower critical solution temperature (LCST)–type phase transition. A series of homo- and block copolymers with varying molar masses but low dispersities and different end groups were prepared. Their thermoresponsive behavior in aqueous solution was analyzed via turbidimetry and dynamic light scattering (DLS). The cloud points (CP) increased with increasing molar masses, converging to 46 °C for 1 wt% solutions. This rise is attributed to the polymers’ hydrophobic end groups incorporated via the RAFT agents. When a surfactant-like strongly hydrophobic end group was attached using a functional RAFT agent, CP was lowered to 42 °C, i.e., closer to human body temperature. Also, the effect of added salts, in particular, the role of the Hofmeister series, on the phase transition of PbMOEAm was investigated, exemplified for the kosmotropic fluoride, intermediate chloride, and chaotropic thiocyanate anions. A pronounced shift of the cloud point of about 10 °C to lower or higher temperatures was observed for 0.2 M fluoride and thiocyanate, respectively. When PbMOEAm was attached to a long hydrophilic block of poly(N,N-dimethylacrylamide) (PDMAm), the cloud points of these block copolymers were strongly shifted towards higher temperatures. While no phase transition was observed for PDMAm-b-pbMOEAm with short thermoresponsive blocks, block copolymers with about equally sized PbMOEAm and PDMAm blocks underwent the coil-to-globule transition around 60 °C.

Synthesis of water-based cationic polyacrylate copolymer emulsion by RAFT polymerization and its application as an inkjet printing agent

PurposeIn this work, the authors used reversible addition-fragmentation transfer (RAFT) polymerization to develop a new cationic acrylate modified epoxy resin emulsion for water-borne inkjet which have the advantages of both polyacrylate and epoxy resin. The emulsion was successfully used in the canvas coating for inkjet printing. This paper aims to contribute to the development of novel cationic emulsions for inkjet printing industry.Design/methodology/approachIn this work, the epoxy acrylate was synthesized from RAFT agent and epoxy resin firstly. Cationic macromolecular emulsifier was prepared by RAFT polymerization, using 2,2’-Azobisisobutyronitrile as initiator, 2-(dimethylamino)ethyl methacrylate and styrene as monomer, which was directly used to prepare the emulsion. The influences of the amount of 2-(dimethylamino)ethyl methacrylate on particle size, zeta potential and water contact angle were studied. Finally, the cationic emulsion was used to print images by inkjet printing.FindingsThe emulsion has the smallest particle size, the highest potential and the highest water contact angle when the DM content is 13 Wt.%. The transmission electron microscopy analysis reveals the latex particles is core-shell sphere with the diameters in the range 120–200 nm. The emulsion was successfully used in the canvas coating for inkjet printing. This work will contribute to the development of novel cationic emulsions for inkjet printing industry.Originality/valueThe emulsion was successfully used in the canvas coating for inkjet printing. This work will contribute to the development of novel cationic emulsions for inkjet printing industry.

Novel poly(3-hydroxy butyrate) macro RAFT agent. Synthesis and characterization of thermoresponsive block copolymers

A novel reversible addition fragmentation transfer (RAFT) agent based on the poly-3-hydroxy butyrate (PHB) with three hydroxyl groups (PHB-R2) and thermoresponsive amphiphilic block copolymers derived from N-isopropyl acryl amide (NIPAM) are described. Hydroxylated PHB is obtained by the reaction between PHB and diethanol amine (DEA) to prepare hydroxylated PHB (PHB-DEA). It is then reacted with a RAFT agent, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT). Hydroxyl ends of the hydroxylated PHB are capped with carboxylic acid end of the trithiocarbonate. The block copolymers obtained by the polymerization of NIPAM initiated by PHB-R2 were characterized by 1H NMR and physicochemical techniques. PHB content in the obtained block copolymers is varying between 14 and 45 wt%. The thermo-responsive PHB-PNIPAM block copolymers show the lower critical solution temperature (LCST) 28 and 30 °C while LCST of the pure PNIPAM is 32 °C.

Tuning the LCST of PNIPAM via Random Oxidation-Sensitive Thioether Functionalities

In this work, an oxidation-responsive thioether-functionalized poly(N-isopropylacrylamide) is reported, which is synthesized via reversible-addition fragmentation transfer (RAFT) polymerization using 6-(methylthio)hexyl acrylate or 2-(methylthio)ethyl acrylate as comonomers and S-ethyl-S′-(a,a′-dimethyl-a″-acetic acid)trithiocarbonate as RAFT agent, investigating the influence over the lower critical solution temperature (LCST) of the random thioether functionalities, prior and upon oxidation. The hydrophobic thioethers shift the LCST values of the resulting copolymers to very low temperatures, but the value could be regulated upon oxidation due to the huge increase in dipolar moment. The resulting copolymers containing hydrophilic sulfoxides show much higher LCST values, reaching a difference of up to 23 °C after oxidation. Results are supported by 1H NMR, size exclusion chromatography, and turbidimetry measurements.

Double network hydrogels with highly enhanced toughness based on a modified first network.

A novel double network (DN) hydrogel with highly enhanced toughness has been prepared using reversible addition-fragmentation transfer (RAFT)-modified poly(2-acrylamide-2-methylpropane sulfonic acid) (PAMPS) as the first network, and polyacrylamide (PAM) as the second network. The mechanical properties of the first-network-modified PAMPS/PAM DN hydrogels have been studied and the new DN hydrogel shows remarkably high fracture energy (3.3 MJ m-3) in tensile deformation, which is nearly 9 times larger than that of the unmodified PAMPS/PAM DN hydrogel. Synchrotron radiation small-angle X-ray scattering (SAXS) was used to study the microstructures of the first-network single network (SN) and DN hydrogels. It was demonstrated by the SAXS results that the introduction of the RAFT agent into the first network enlarges the size of the ordered cross-linked domains in the SN hydrogel. The large ordered domains are beneficial for entanglement and interpenetration between the first and the second networks to dissipate concentrated stress more efficiently, resulting in the enhanced toughness of the first-network-modified DN hydrogels.

Dithiobenzoic copper(II): A novel, facile, and stable mediating agent combining ATRP and RAFT features for reversible deactivation radical polymerization of methacrylates

Novel, facile, and stable mediating agent (dithiobenzoic copper(II)) combining atom transfer radical polymerization (ATRP) and reversible addition fragmentation transfer (RAFT) characteristics was firstly designed by replacing the halogen of ATRP metal catalyst with thiocarbonyl carboxylic group of RAFT agent. As two kinds of mediating agents (ATRP activator and RAFT agent) may be formed in situ during the polymerization process, the polymerization of various methacrylates can be controlled in presence of a high molar ratio of radical initiator to catalyst. Furthermore, the resultant polymer possessed dithiobenzoate chain-end functional group, which was confirmed by IH NMR analyses and chain-extension reaction.

Modeling of Highly Branched Water‐Soluble Polymers with Applications to Drug Delivery Model Extensions and Validation

Reversible addition fragmentation transfer (RAFT) polymerization can be used to produce highly branched polymer approximating the structure of dendrimers, but with less regularity and much less synthetic complexity. This can be accomplished by using a RAFT agent with a polymerizable double bond. Thus, the stoichiometry is fixed, with one branch point (RAFT agent double bond) per chain. Since each of these branch points will also branch, a highly regular highly branched material is formed. If this RAFT chemistry is applied to the monomer N‐isopropyl‐acrylamide (NIPAAm), the resulting water‐soluble polymer has unique applications in drug delivery, due to the hyperbranched nature of the polymer, and also to the lower critical solution temperature exhibited by poly(NIPAAm). In this paper, a previous mathematical model of the RAFT‐pNIPAAm system is extended, and validated against experimental polymerization data.

Kinetic investigations of RAFT polymerization: Difunctional RAFT agent mediated polymerization of methyl methacrylate and styrene

A difunctional reversible addition-fragmentation transfer (RAFT) agent, S,S’-bis (α,α’-dimethylacetic acid) trithiocarbonate (BDAT) is synthesized and used as chain transfer agent (CTA) to mediate homopolymerization of methyl methacrylate (MMA) and random copolymerization of methyl methacrylate-styrene (St) system, respectively. Kinetic factors of these two polymerizations, which influence polymerization process and characteristics of polymers, are investigated. Experimental results show that molecular weights of polymers increase linearly with monomer conversions and these two polymerization kinetics behaviors exhibit “controlled/living” characteristics. For the homopolymerization of MMA, molecular weights increase gradually and are close to their theoretical values. Wherever, for the random copolymerization of MMA-St system, the presence of St has important influence on the kinetics of copolymerization. Addition of St to this system induces an induction period and this period increase with increasing content of St in monomer composition.

PH-responsive non-ionic diblock copolymers: ionization of carboxylic acid end-groups induces an order-order morphological transition.

A carboxylic acid based reversible additionfragmentation transfer (RAFT) agent is used to prepare gels composed of worm-like diblock copolymers using two non-ionic monomers, glycerol monomethacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA). Ionization of the carboxylic acid end-group on the PGMA stabilizer block induces a worm-to-sphere transition, which in turn causes immediate degelation. This morphological transition is fully reversible as determined by TEM and rheology studies and occurs because of a subtle change in the packing parameter for the copolymer chains. A control experiment where the methyl ester derivative of the RAFT agent is used to prepare the same diblock copolymer confirms that no pH-responsive behavior occurs in this case. This end-group ionization approach is important for the design of new pH-responsive copolymer nano-objects as, unlike polyacids or polybases, only a minimal amount of added base (or acid) is required to drive the morphological transition.

PH‐Responsive Non‐Ionic Diblock Copolymers: Ionization of Carboxylic Acid End‐Groups Induces an Order–Order Morphological Transition

AbstractA carboxylic acid based reversible additionfragmentation transfer (RAFT) agent is used to prepare gels composed of worm‐like diblock copolymers using two non‐ionic monomers, glycerol monomethacrylate (GMA) and 2‐hydroxypropyl methacrylate (HPMA). Ionization of the carboxylic acid end‐group on the PGMA stabilizer block induces a worm‐to‐sphere transition, which in turn causes immediate degelation. This morphological transition is fully reversible as determined by TEM and rheology studies and occurs because of a subtle change in the packing parameter for the copolymer chains. A control experiment where the methyl ester derivative of the RAFT agent is used to prepare the same diblock copolymer confirms that no pH‐responsive behavior occurs in this case. This end‐group ionization approach is important for the design of new pH‐responsive copolymer nano‐objects as, unlike polyacids or polybases, only a minimal amount of added base (or acid) is required to drive the morphological transition.

Overcoming a Tight Coil To Give a Random “Co” Polymer Derived from a Mixed Sandwich Cobaltocene

Reversible addition–fragmentation transfer (RAFT) polymerization of a η5-cyclopentadienylcobalt-η4-cyclobutadiene (CpCoCb) containing monomer under a wide variety of experimental conditions (e.g., different solvents, temperatures, RAFT agents, concentrations, and [RAFT agent]/[initiator]) was examined. In all cases the results revealed that although the monomer was being consumed over the course of the reaction, there was no significant increase in the molecular weight of the resulting polymer. It was determined that as the polymer chain grows (DP ≈ 10), a tight coil morphology was adopted, which hinders the approach of an additional, sterically demanding CpCoCb-containing monomer. This resulted in premature termination/chain transfer reactions rather than an increase in the polymer chain length. To address this problem, methyl acrylate (MA) with its lower steric demand was copolymerized with the bulky CpCoCb-containing monomer to act as a spacer. This provided the necessary steric relief and an opportuni...

Synthesis of fluorinated gradient copolymers by RAFT emulsifier-free emulsion polymerization and their compatibilization in copolymer blends

The gradient copolymers of styrene and fluorinated acrylate were synthesized by reversible addition-fragmentation transfer (RAFT) emulsifier-free emulsion polymerization under the control of amphiphilic RAFT agent. The polymerization conditions were studied in detail. Molecular weights were traced by gel permeation chromatography (GPC) during the polymerization process. The copolymer structures were characterized by 1H NMR, Fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). These results proved that the copolymer had a gradient chain structure. The gradient copolymer was used as a compatibilizer to improve the compatibility of the polystyrene/fluoropolymer blend. The effects of molecular weight and adding content of the gradient copolymer on the compatibilization were studied.

Targeting Copolymer Composition Distribution via Model-Based Monomer Feeding Policy in Semibatch RAFT Mini-Emulsion Copolymerization of Styrene and Butyl Acrylate

Copolymer composition distribution (CCD) is an important parameter of chain microstructure that has significant impact on the material properties of polymer products. Controlled/living radical polymerization (CLRP) has provided a great opportunity in producing polymers with predesigned CCDs through a model-based monomer feeding policy (MMFP) in homogeneous systems. In this work, the MMFP has been expanded to heterogeneous systems. Reversible addition–fragmentation transfer (RAFT) mini-emulsion polymerizations of styrene (St) and butyl acrylate (BA) were carried out with 3-benzyltrithiocarbonyl propionic acid (BCPA) used as a RAFT agent. A kinetic model was developed and correlated to the batch St/BA RAFT mini-emulsion experimental data for parameter estimation. The MMFP was then developed by combining the kinetic model with a semibatch reactor model and applied to the semibatch St/BA RAFT mini-emulsion copolymerization for the synthesis of targeted CCDs. The model agreed well with the polymerization kinetics. A series of St/BA copolymers with predesigned CCDs were successfully synthesized.

One-pot synthesis of POSS-containing alternating copolymers by RAFT polymerization and their microphase-separated nanostructures

The poly(styrene-alt-maleimide isobutyl POSS) (PSMIPOSS) alternating copolymer is one-pot synthesized via reversible addition-fragmentation transfer (RAFT) polymerization. The results show that a POSS-containing alternating copolymer with a high degree of polymerization (DP) and a low polydispersity index (PDI) is successfully constructed by alternating copolymerization of maleimide isobutyl POSS with styrene, and the molecular weight of the PSMIPOSS alternating copolymer can be well controlled by the amount of RAFT agent. Poly(styrene-alt-maleimide isobutyl POSS)-block-polystyrene (PSMIPOSS-b-PS) block copolymers are also one-pot prepared by RAFT polymerization, and their self-assembly behavior in the bulk is investigated by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS), which exhibit a series of short-range order phase transitions from the POSS sphere, POSS cylinder to lamella structures with the weight fraction of MIPOSS ranging from 13% to 64%. The thermal properties of POSS-containing copolymers are evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The results display that MIPOSS units can enhance the thermal properties of copolymers effectively.

Facile design of degradable poly(β‐thioester)s with tunable structure and functionality

ABSTRACTThe synthesis of a range of linear biodegradable poly(β‐thioester)s, PBTs, via hexylamine‐catalyzed thiol‐ene Micheal additions between a variety of diacrylate and dithiol monomers is described. Molecular weights up to 12,000 g mol−1 are obtained for this new class of polymer materials. PBTs featuring very different chemical and mechanical behavior are obtained on the basis of seven diacrylate and three dithiol monomers. Polar PBTs are synthesized based on ethylene glycol‐containing monomers in an environmentally friendly solvent. Furthermore, PBTs containing urethane units in the main chain are obtained, providing access to an isocyanate‐free polyurethane polymerization method. The thiol‐ene addition approach can also be used to couple polystyrene oligomers synthesized from a bifunctional trithiocarbonate reversible addition fragmentation transfer agent. In this way, PBTs featuring polystyrene segments as well as diacrylate segments are produced. In general for these step‐growth polymerizations, by tuning the stoichiometric monomer ratio, a desired end group functionality can be quantitatively introduced into the PBT, which is demonstrated via soft ionization mass spectrometry analysis. As an example, alkyne end groups have been built in, giving access to use these materials in modular polymer design strategies. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 178–187

RAFT controlled synthesis of graphene/polymer hydrogel with enhanced mechanical property for pH-controlled drug release

A pH-sensitive, mechanically strong and thermally stable graphene/poly (acrylic acid) (graphene/PAA) hydrogel was prepared via reversible addition fragmentation transfer (RAFT) polymerizations in the presence of a cross-linking agent. The RAFT agent was covalently coupled onto graphene basal planes via an esterification reaction, with benzoic acid functionalities pre-attached on graphene with its aryl diazonium salt precursor. AFM and SEM analysis revealed the successful preparation of single layered graphene sheets and graphene/polymer hydrogels with pH controlled porous structures. Attenuated total reflection infrared (ATR-IR) and thermogravimetric analyzer (TGA) verified the successful stepwise preparation of graphene/PAA hydrogel. This graphene/PAA hydrogel was pH-sensitive and more mechanically elastic than the PAA hydrogel prepared without graphene. The pH sensitivity of the hydrogel was further utilized for controlled drug release. Doxorubicin was chosen as a model drug and loaded into the hydrogels. The drug loading and release experiment indicated that this hydrogel can be used to efficiently control drug release in the intestine environment (pH=7.4), better than release in a more acidic environment.

Synthesis, characterization, and self‐assembly of amphiphilic fluorinated gradient copolymer

AbstractAn amphiphilic copolymer of acrylic acid (AA) and 2,2,2‐trifluoroethyl methacrylate (TFEMA) was synthesized by reversible addition‐fragmentation transfer (RAFT) copolymerization, using a feed method for adding TFEMA. The kinetics of the RAFT copolymerization agreed well with those characteristic of a first‐order reaction and the molecular weight of copolymers increased with the conversion increasing, both demonstrating that it proceeded in a controlled polymerization manner. Optimal copolymerization was achieved when the reaction was conducted at 70°C, using a molar ratio of TFEMA : AA : RAFT agent : initiator of 400 : 400 : 4 : 1. Analysis of instantaneous 1H‐NMR results proved that the obtained copolymer had a chain structure with AA segments gradually changing to TFEMA segments. The copolymer films had lower surface free energies and slightly microphase separation structures. The amphiphilic copolymer with gradient structures could self‐assemble to form aggregates in selective solvents. The type and composition of solvent mixtures had great effects on the morphology and sizes of aggregates, which were investigated by transmission electron microscopy and dynamic light scattering, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013